The present invention relates to extensible articles, methods for making such articles and to methods of assessing the degree of extension of such articles.
For many extensible articles it is desirable to be able to assess when a pre-determined degree of extension has been achieved. For example it may be desirable to know when a particular material has been extended to a value which is close to its elastic limit in order to avoid exceeding said limit.
In the field of medicine, extensible fabrics are often used in dressings and bandages and if these are applied too tightly to a patient problems may result due to the high pressure applied. In extreme cases blood flow can be severely impaired and damage to body tissues can result.
This is a problem which is well known and which has existed for many years in the field of bandages.
Woven or knitted elastic bandages in both adhesive and nonadhesive forms are used to provide support, to assist in the healing of strained muscles and in the treatment of various venous conditions. Conventional elasticated woven or knitted bandages have one or more warp yarns which comprise elastomeric materials such as natural rubber or synthetic elastomeric materials such as polyurethane. It is important that these bandages are applied at a tension which is sufficiently high to enable them to maintain an effective level of compressive force under the bandage over a period of time.
U.S. Pat. No. 4,653,492 discloses an elastic bandage having a resilient elastic layer and a relatively non-resilient elastic layer to limit the stretching of the elastic layer so the bandage is not applied too tightly.
U.S. Pat. No. 4,366,814 discloses an elastic bandage material comprising at least 50 percent by weight of an extensible fabric capable of elongation of at least 30 percent without tearing and at least 15 percent of an elastomer impregnated in a fabric. The bandage material is said to be especially suited for use as a backing for adhesive tapes and dressings.
Patent application no FR-A-2,542,201 discloses a surgical support which is said to be extensible in all directions and impermeable to liquids, characterized in that it comprises a polyurethane film and a non-woven elastomeric material which is stretchable in all directions and which penetrates through the thickness of the polyurethane film, the fibers of the non-woven material each having a length greater or equal to 6 cm. The surgical support is of use in the field of wound dressings. It is prepared by depositing a polyurethane containing liquid composition on a temporary support, introducing in situ the non-woven material. and then drying.
However, a disadvantage associated with the known woven or knitted bandages discussed above is that if they are stretched too much during the application, the compression force under the bandage may be too much and cause damage, for example by restriction of the blood supply.
In order to alleviate these problems it is known to mark bandages with markings which adopt a particular identifiable configuration when a bandage has been stretched to a certain degree. Such bandages are disclosed in U.S. Pat. No. 3,613,679, Patent application nos EP 0,475,811, DE 3,640,979 and DE 2,329,371. Thus when the particular configuration is achieved, a person applying the bandage may determine visually that a desired degree of extension has been achieved. For example. it is known to provide compression bandages having markings which appear as squares when a planar bandage is stretched to a desired degree and which in an unstretched state appear as narrow rectangles.
However, these bandages suffer from the disadvantage that it is often difficult to assess when a desired degree of extension has been achieved.
This is because bandages are applied by different users in different manners and therefore there is considerable variation between users in the degree of overlap of layers of bandage, the angle at which the bandage is applied relative to a longitudinal axis along a body member, etc. Furthermore limbs are irregular in shape and vary considerably from patient to patient.
Patent Application No. WO94/12133 discloses a bandage with a geometrical image knitted into the bandage where the image configuration changes on stretching.
Patent application no DE 2,329,371 additionally discloses a bandage with a creased indicator glued onto the bandage which extension on the bandage unfolds.
However the preparation of such a bandage requires a lengthy process incorporating a number of steps. Additionally such bandages are not as soft and easy to apply.
There is thus a need to provide an effective, convenient and inexpensive way of determining when an extensible article (e.g. an elastic bandage) has been extended to a particular degree.